high compression pistons, forges rods, port matching, intake (not just a cai or short ram) cams along with valves and springs, turbo or supercharger. but all of these modifications are pricey, and if not done right or you don't have the supporting mods you'll just end up with an unreliable motor, and thats no fun. What ever you decide to do make sure your engine components can handle the extra power, and pay a little bit more for the right parts.